In typical commercial reproduction apparatus (electrostatographic copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive fuser roller having dielectric characteristics (hereinafter referred to as the dielectric support fuser roller). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric support fuser roller. A receiver fuser roller, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support fuser roller, and an electric field applied to transfer the marking particle developed image to the receiver from the dielectric support fuser roller. After transfer, the receiver bearing the transferred image is transported away from the dielectric support fuser roller, and the image is fixed (fused) to the receiver by heat and pressure to form a permanent reproduction thereon.
One type of fuser assembly for typical electrographic reproduction apparatus includes at least one heated roller, having an aluminum core and an elastomeric cover layer, and at least one pressure roller in nip relation with the heated roller. The fuser assembly rollers are rotated to transport a receiver, bearing a marking particle image, through the nip between the rollers. The pigmented marking particles of the transferred image on the surface of the receiver soften and become tacky in the heat. Under the pressure, the softened tacky marking particles attach to each other and are partially imbibed into the interstices of the fibers at the surface of the receiver. Accordingly, upon cooling, the marking particle image is permanently fixed to the receiver.
With roller fuser assemblies, it is common practice to use release fluids, such as silicone oil for example, applied to the fuser roller surface to improve the release of image-carrying receivers from the fuser roller. The most common types of release fluid applicators or oilers are a rotating wick roller, a donor/metering roller, an oil impregnated oiling web, oil impregnated oiling pad or roller, or variations or combinations of the above. The release oil applied to the fuser roller tends to migrate from the fuser roller to the opposing pressure roller. This occurs, for example, between receivers passing through the fuser assembly. Oil on the pressure roller can be deposited on subsequent receivers transported through the fuser assembly. This may lead to undesirable, deleterious artifacts on the copies being reproduced, such that the copies are degraded to the extent that makes them unacceptable for intended use.
The fusing step in a roller fuser commonly consists of passing the toned receiver between a pair of engaged rollers that produce an area of pressure contact known as a fusing nip. In order to form the fusing nip, at least one of the rollers typically has a compliant or conformable layer on its surface. Heat is transferred from at least one of the rollers to the toner in the fusing nip, causing the toner to partially melt and attach to the receiver. In the case where the fuser roller is a heated roller, a resilient compliant layer having a smooth surface is typically used which is bonded either directly or indirectly to the core of the roller. Where the fuser roller is in the form of a belt, e.g., a flexible endless belt that passes around the heated roller, it typically has a smooth, hardened outer surface.
Most roller fusers, known as simplex fusers, attach toner to only one side of the receiver at a time. In this type of fuser, the roller that contacts the unfused toner is commonly known as the fuser roller and is usually the heated roller. The roller that contacts the other side of the receiver is known as the pressure roller and is usually unheated. Either or both rollers can have a compliant layer on or near the surface. In most fusing stations having a fuser roller and an engaged pressure roller, it is common for only one of the two rollers to be driven rotatably by an external source. The other roller is then driven rotatably by frictional contact.
In a duplex fusing station, which is less common, two toner images are simultaneously attached, one to each side of a receiver passing through a fusing nip. In such a duplex fusing station there is no real distinction between fuser roller and pressure roller, both rollers performing similar functions, i.e., providing heat and pressure.
Two basic types of simplex heated roller fusers have evolved. One uses a conformable or compliant pressure roller to form the fusing nip against a hard fuser roller, such as in a DocuTech 135 machine made by the Xerox Corporation. The other uses a compliant fuser roller to form the nip against a hard or relatively non-conformable pressure roller, such as in a Digimaster 9110 machine made by the Eastman Kodak Company. A fuser roller designated herein as compliant typically includes a conformable layer having a thickness greater than about 2 mm and in some cases exceeding 25 mm. A fuser roller designated herein as hard includes a rigid cylinder, which may have a relatively thin polymeric or conformable elastomeric coating, typically less than about 1.25 mm thick. A compliant fuser roller used in conjunction with a hard pressure roller tends to provide easier release of a receiver from the heated fuser roller, because the distorted shape of the compliant surface in the nip tends to bend the receiver towards the relatively non-conformable pressure roller and away from the much more conformable fuser roller.
A conventional toner fuser roller includes a cylindrical core, often metallic such as aluminum, coated with one or more synthetic layers, which typically include polymeric materials made from elastomers. Some fusing assemblies also includes a release fluid application subassembly that applies release fluid, such as, for example, silicone oil, to fusing roller. The release fluid substantially prevents toner particles from sticking to the fuser roller.
One common type of fuser roller is internally heated, i.e., a source of heat for fusing is provided within the roller for fusing. Such a fuser roller normally has a hollow core, inside of which is located a heating source, usually a lamp. Surrounding the core is an elastomeric layer through which heat is conducted from the core to the surface, and the elastomeric layer typically contains fillers for enhanced thermal conductivity. A different kind of fuser roller, which is internally heated near its surface, is disclosed by Lee et al. in U.S. Pat. No. 4,791,275, which describes a fuser roller including two polyimide Kapton® sheets (sold by DuPont.®. and Nemours) having a flexible ohmic heating element disposed between the sheets. The polyimide sheets surround a conformable polyimide foam layer attached to a core. According to J. H. DuBois and F. W. John, Eds., in Plastics, 5th Edition, Van Nostrand and Rheinhold, 1974, polyimide at room temperature is fairly stiff with a Young's modulus of about 3.5 GPa-5.5 GPa (1 GPa=1 GigaPascal=10.sup.9 Newton/m.sup.2), but the Young's modulus of the polyimide sheets can be expected to be considerably lower at the stated high operational fusing temperature of the roller of at least 450 degrees F. Alternately an externally heated fuser roller may be used, for example, in an Image Source 120 copier, and can be heated by surface contact between the fuser roller and one or more external heating rollers or other means. Externally heated fuser rollers are also disclosed by O'Leary, U.S. Pat. No. 5,450,183, and by Derimiggio et al., U.S. Pat. No. 4,984,027.
The fixing quality of toned images of an electrophotographic printer depends on the temperature, nip-width, process speed, and thermal properties of the fusing roller, toner chemistry, toner coverage, and receiver type. To simplify the engineering and control of a roller fusing system, as many as possible of the above parameters are considered and then fixed during the system's design. The fusing parameters such as temperature, nip-width, process speed, and thermal properties of the fusing roller are optimized for the most critical case.
Complicating the system's design is the fact that the toner coverage and the receiver type (weight, coated/uncoated) can vary from image to image in a digital printer. Therefore, some of the above listed parameters need to be adjusted according to the image contents and the receiver types to assure adequate image fixing. Typically, the fuser temperature is adjusted and kept constant for a dedicated run with a particular receiver. The temperature is adjusted higher from the nominal for heavier receivers and lower for lighter receivers. For some heavy receivers, the speed must also be reduced.
In the standard fusing system the pressure roller and/or the interframe area can become contaminated with oil and this causes problems with image quality. One way this occurs is due to the application of the release fluid, such as, for example, silicone oil, to fusing roller to prevent toner particles from sticking to the fuser roller. If there is excess oil then some remains in the interframe areas between sheets of receivers and cause artifacts on the next printed receivers. In order to reduce image artifacts which are attributable to and/or are the result of release fluid disposed upon and/or impregnating a receiver that is subsequently processed by/through another device such as a glossing assembly there is the need for a interframe cleaning device.